Many hearing challenged people, with or without hearing aids, experience difficulties hearing in noisy situations (e.g., face-to-face communications in restaurants with a lot of competing voices). Even typical hearing aids do not alleviate the problem, since in noisy situations the hearing aids amplify not only the desired signal but also the ambient noise. There are also situations, where the speech is simply too faint to be heard without any assistive listening (or listening assistance) devices regardless whether the person (listener) has a hearing impairment or not.
Assistive listening devices are commonly used to alleviate the problem. The main idea behind assistive listening devices is to amplify one signal of interest with respect to a background noise by bringing the microphone closer to the desired source. The improvements in a signal-to-noise ratio can, in practical situations, be as high as 15 to 20 dBs (decibels). The assistive listening devices can be divided into four groups:
1. Personal listening systems, which are ideal for use in small group situations, car trips, noisy restaurants, or any place where there is a distracting environmental noise. There are wired and wireless versions and they typically consist of a microphone unit to be positioned closer to the talker and a headphone (or earphone).
2. FM systems, which are ideal for situations which require a higher distance of operation, such as classrooms, meetings, conferences and trainings. They consist of, e.g., a microphone unit and a small body worn transmitter to be given to a lecturer, and a receiver unit with headphones to be worn by a user. The receivers can also be used with a hearing aid (assuming the hearing aid has a T-coil switch and/or a direct audio input). The FM systems are much more expensive.
3. Group listening systems, which consist of one transmitter system and several receiver systems.
4. TV listening systems, where the transmitter connects directly to a TV/VCR audio output. For example, Sennheiser manufactures currently wireless headphones with an automatic gain control and a tone adjustment.
Hearing aids with directional microphones are useful by providing some spatial discrimination to the amplification, but the amount of SNR (signal-to-noise ratio) improvement is significantly lower than with aforementioned assistive listening devices.